Chris - I see that you edited my text a bit. Nice job. And nice job loading it onto the wiki. You must be a wiki editing animal. I'll PM you. You know, its much easier to describe things in forum threads. In the Arducopter document, it has to be very close to accurate .....just kidding.. I'll help where I can.

Thank you Lloyd, You have been very helpfull. I have done most of what you explained but the cutting of the jumper trace. This jumper trace already comes cut as default or are my eyes getting weaker? I actually thought that this trace would have to be connected by a blob of solder??

Frank - you have to cut the trace. I received the picture and hint at what do from 3DR customer service.

Cutting the trace cuts the SDA line, which means the magnetometer cannot be selected. So you have to cut it. I know its hard to see, but I just bore down on the knife while cutting to penetrate the board a little.

I've installed an external magnetometer on my quadcopter using your manual, but I'm not entirely sure if it's working like it should.

The manual states that it's required to cut a small jumper trace on my APM 2.5 main board. I tried to do this, but am not sure if applied enough force. Is there a way to use the MP software to establish if I rendered the onboard compass inert?

First - take an ohmmeter reading between the two pads that you cut the trace between. If you cut the trace, you will see an ohm reading of much more than 0 ohms - like many thousand or even millions of ohms. You will see 0 ( or a few ohms depending on your ohmmeter calibration) if the trace is still intact. If you don't have a volt-ohmmeter, I would by one. They are very handy and can be very low cost.

Second, I would check if the on-board compass is still working without an external compass connected. So with the external compass disconnected, go into the CLI and type "test" and then "compass". Rotate the APM 2.5 and if the first number, which is the compass reading, changes with APM direction, then the trace is still connected. Take a magnifying glass and look real carefully at the trace. If the number does not change as you change the APM's direction, then it must be cut.

The final test is to connect the external compass to the APM 2.5, go into the CLI and re-run t"test" and then "compass". The first number is the magnetic direction. It should correspond to the direction the external compass is pointing. 0 for north, 90 for west, 180 for south and 270 for west. If the reading corresponds to those numbers, then it it working. I suppose if the readings sort-of, kind-of reads the right direction, or the reading doesn't change, then you might still have the trace intact (you're getting readings from both compasses).

I do not understand what you mean by putting the APM board along two sides of a book.

If you point the APM board (input pins forward) toward North, do you see 0 (or thereabouts) on the CLI? If you then point the APM west, do you see 270? and 180 when point south and 90 when pointed east?